Cleanup the tox configuration and requirements.
Black formatter was applied in the modified files.
Test Plan:
Verify that all Tox tests pass without errors.
1. Successfully executed on the distributedcloud dir
- tox -e docs,releasenotes,api-ref,bandit,linters
- tox -e newnote -- new-note
2. Successfully executed on the distributedcloud/distributedcloud dir
- tox -e py39,pylint,pep8,cover
Partial-Bug: 2053023
Change-Id: Ib25f31f8607e46e51dfbda0a6b3a36e9e11151df
Signed-off-by: Hugo Brito <hugo.brito@windriver.com>